(a) Field of the Invention
The present invention relates to the construction of a sliding throttle-valve type carburetor.
(b) Prior Art
In the conventional design of carburetors, it is usual to make the fuel passages extend perpendicularly to the fuel surface in the float chamber and to dispose the air intake passage parallel to the fuel surface, in order to simplify the fuel passage arrangement and to compensate for changes in the closing force of the float valve caused by the displacement of the center of the fuel surface due to a change in the fuel surface attributable to forward or backward inclination of the vehicle. In some cases, however, conditions such as the arrangement and mounting angles of the cylinders of the engine require the air intake passage to be at an inclination relative to the fuel surface due to restriction of the space for accommodating the air intake pipe and the like. In such a case, and with reference to FIG. 10, if a sliding throttle valve 12 and a float chamber 15 are arranged perpendicularly to the fuel surface l with respect to the inclined intake passage 14, the sliding throttle valve 12 interferes with the portion of the air intake passage upstream from the sliding throttle valve 12 in the region A, while the portion of the passage 14 downstream from the sliding throttle valve 12 interferes with the float chamber 15 in the region B. To avoid this problem, it is necessary to increase the overall length of the intake passage 14 and to lower the float chamber 15. However, the length of the intake system of the internal combustion engine should be small in order to reduce the intake resistance, and is determined also by the intake inertia charging effect. It is quite difficult to vary the length of the intake passage of the carburetor (constituting a part of the intake system of the engine) without adversely affecting the performance of the engine. The increase of the length of the intake passage is also limited for reasons concerning installation.
If the intake passage 14 of the carburetor is arranged to cross the sliding throttle valve 12 at a sufficiently large angle, interference occurs in the region C (FIG. 11) and the fuel surface must be positioned at a higher level whereby the fuel system is not adapted for forward inclination.
As a countermeasure for eliminating the undesirable effect of the inclination, it is considered to arrange the fuel passage at right angles to the fuel surface as seen in FIG. 12. In such case, however, it is necessary to deflect the main fuel passage towards the inclined intake passage, so that the construction is complicated, particularly in a carburetor having a fuel metering needle valve 33 resulting in a large resistance encountered by the fuel flowing in the fuel passage, which produces various problems such as vapor lock, percolation and the like due to inferior relief of the fuel vapor.